No. 121 

1961 

RESULTS OF DEER EXCLOSURE STUDIES 

IN NORTHEASTERN PENNSYLVANIA 

To ddonstrate how deer browsing affects natural tree 

seedling and sprout reproduction, two groups of deer exclosures were established in the Pocono Mountains of northeastern Pennsylvania. Study of these exclosures after seven 

growing seasons confirms what other studies elsewhere have 

found: that when deer are too numerous for their natural 

food supply, it is impossible to achieve a balanced multiple 

use of forest land for both timber production and wildlife 

habitat. 

The Installations 

Strips through young oak-maple stands had been clearcut, except for an occasional oak left for mast, by the 

State Game Commission in February 1953. The purpose was to 

provide deer browse: felled trees were not completely severed, but were left hinged to the stumps to prolong life in 

the crowns for browsing. 

The exclosures were built about 3 months later in 

these clear-cut strips. Bulky slash was removed to facilitate the fencing job and the later examinations for seedlings. Each of the two groups of exclosures consisted of 

three 1/40-acre square plots--two contiguous ones surrounded 

by 8-foot fence and one open check plot. The check plots 

were located 10 or more feet from the other plots so as not 

to be affected by deer trailing around the fences. 
NUMBER OF TREES PER ACRE 

Figure 1.--Number of seedlings per acre, by height or d.b.h. 

class, outside and inside exc losures. 
Figure 2.--A check plot, showing form and growth of 

seedlzngs and sprouts. 

One of each fenced pair of plots originally was rabbit-proofed with fine wire netting, but the netting broke 

down or was disturbed by vandals, so the fenced plots can be 

considered as duplicates, excluding deer only. 

Results 

After seven growing seasons (fall of 1959), developments at the two plot locations were similar, so the data 

are combined in the following summary of results: 

a Seedlings generally were more numerous in the fenced 

plots than in the open check plots; this was particularly 

true of the size classes larger than 2 feet tall (fig. 1). 

The considerable numbers of 1- to 1.9-foot seedlings on the 
Figure 3.--Dense aspen reproduction inside an exclosure 

at the same location as check plot shown in Figure 2. 
check plots included many stems that had been browsed back 

but not killed--stems that otherwise would have grown into 

larger sizes. 

Differences between fenced and check plots--that is, 

browsing ef fects--were most marked on aspen, sassafras, hawthorn, and the viburnums. Aspen was completely eliminated 

from the check plot in the one location where it occurred 

(fig. 2)) whereas a dense stand developed where protected 

inside the fence (fig. 3). That this was a true treatment 

effect, and not explainable by a dearth of initial stocking 

of aspen on the check plot, was shown by interim tallies: 

4,600 aspen stems per acre in 1954; down to 39 stems per 

acre in 1957; and none in 1959. 

Numbers of sprout clumps were not markedly affected by 

exposure to browsing, except, possibly, serviceberry and 

hawthorn. Evidently browse was plentiful enough locally, as 

a result of the 1953 cuttings, so that sprout clumps generally were able to survive. 

a Although numbers of sprout clumps were little affected by 

browsing, average numbers of stems per clump, average 

heights, and average crown spreads were substantially reduced (fig. 4). Sprouts of the more desirable species, such 

as white oak and red maple, were almost twice as tall inside 

the exclosures as on the check plots. 

The growth form of both seedlings and sprouts outside the 

exclosures was generally shrubby and misshapen from repeated browsing (fig. 2)) as compared to the normal, reasonably straight stems of the same species found inside the 

fences (fig. 3). 

Discussion 

Because of the browse cutting in 1953 and subsequent 

sprouting, considerable deer food was available locally, and 

the destructive effects of deer on commercial timber species 

were not so striking as may sometimes be seen. Some stems 

gradually were getting above deer's reach and will form some 

sort of forest stand. 

The elimination of aspen points up the effect that 

deer often have on beaver and other wildlife. Aspen is the 

most important food of beaver in the Northeast (Martin, et 

a. 195. And it has of ten been observed that, where beaver fell aspen in overpopulated deer ranges, suckers that 

 artin in, Alexander C., Zim, Herbert S., and Nelson, Arnold L. American wildlife and plants. 500 pp., illus. NewYork, London. 1951. 
V --- 

BEECH SERV ICE HAWTHORN WHITE RED CHESTNUT SASSAFRAS RED AND GRAY 

BERRY OAK MAPLE SCARLET OAK BIRCH 
would normally replace these felled trees are eliminated by 

deer browsing, and the beaver move out. 

In a normal selective timber-cutting operation, excessive deer herds could be expected to have an even greater 

influence on reproduction than on our study areas because 

less browse would be produced. Even where browse is abundant and regeneration is able eventually to form a closed 

stand, a heavy deer population can str.ongly influence the 

quality and composition of the new forest with respect to 

both timber and wildlife habitat values. 

--E. L. SHAFER, Jr., T. J. GRISEZ, and ED SOWA 

Northeastern Forest Experiment Station 

Forest Service, U.S. Dept. Agriculture